The present invention provides novel reaction products of sulfur dioxide and a material containing both vinyl ester groups and 1,2-epoxy groups.
Preparation of epoxy resin and sulfur dioxide copolymers in the presence of an oxidizing agent which is capable of reacting with sulfur dioxide to form a catalyst for curing said epoxy resin is taught by W. D. Woodson in U.S. Pat. No. 4,518,723. Within the scope of the teachings of Woodson is the addition of monomeric materials including acrylic or vinyl monomers to the acid-curable epoxy resin followed by copolymerization with sulfur dioxide in the presence of an oxidizing agent.
G. Vanhaeren and G. B. Butler in Polymer Preprints, Volume 6, Number 1, pages 709-715, April 1965 polymerized acrylic acid or acrylamide with sulfur dioxide in the presence of t-butylhydroperoxide. Both reactions yielded only pure homopolymer, poly(acrylic acid) or poly(acrylamide), respectively, with only a trace of sulfur incorporation into the homopolymer, probably as the initiator (p. 714). It was observed that the polysulfone (copolymer with sulfur dioxide) of acrylic acid and acrylamide could not be obtained by free radical copolymerization in liquid sulfur dioxide because they had no donor-acceptor interaction of electrons with sulfur dioxide. In a low temperature reaction, acrylic acid and acrylamide gave a "flash" polymerization.
The present invention pertains to reaction products of sulfur dioxide with a material containing both vinyl ester groups and 1,2-epoxy groups. The compositions of the present invention provide an improvement in one or more of the properties selected from pencil hardness, surface tack reduction, methylethylketone resistance and impact resistance when compared to reaction products of sulfur dioxide with a vinyl ester of a di- or polyepoxide (contains two or more polymerizable ethylenically unsaturated groups per molecule). Furthermore, the compositions of the present invention provide the ability to thermally postcure thin film coatings thus giving improved properties when compared to reaction products of sulfur dioxide with an epoxy resin.
As a further advantage of the present invention, reaction products formed using mixtures of at least one material having at least one vinyl ester group and at least one 1,2-epoxy group per molecule, a material containing two or more 1,2-epoxy groups and a vinyl ester (containing two or more polymerizable ethylenically unsaturated groups) with sulfur dioxide provide a polymer network wherein under reaction conditions which form a homopolymer of the vinyl ester, chemical bonding of this homopolymer into the polymer network occurs. By way of contrast, when mixtures containing two or more epoxide groups, such as an epoxy resin, and a vinyl ester are polymerized with sulfur dioxide under reaction conditions which form a homopolymer of the vinyl ester, little, if any, chemical bonding of the homopolymer to the polymer network formed from polyepoxide and sulfur dioxide occurs. This can lead to decreased mechanical properties as well as migration, increased extractability or phase incompatibility of the homopolymer.